Bulk products, including powders or granulates such as flour, sand and coffee, as well as larger items such as nuts or potatoes are often stored in large containers and unloaded therefrom through egress openings in the bottom of the containers. Such containers are often designed to have very steep walls adjacent the egress opening to aid the outward flow of the bulk material. Nevertheless the material often becomes clogged and will not flow out of the container. This phenomenon is generally termed "bridging" since the bulk material tends to assume a curved or cupola-like shape. It is known that sometimes vibrating or knocking the container walls from outside is sufficient to "break the bridge" of bulk material and enable the flow to recommence. Sometimes, however, such vibrating or knocking results in container wall vibrations which further compact the material resulting in an even more rigid and indestructable bridge being formed.
It is believed that the particles of bulk material tend to interact in a self-locking position. The mechanical definition of self-locking refers to a situation wherein particles cannot move relative to each other in the direction of an applied driving force component, such as gravity, due to the presence of a force such as a frictional force component which is larger than the driving force component and normal thereto and which urges the particles against each other. The frictional force component that holds the particles together is proportional to the coefficient of friction of the particular bulk material. Thus, materials having relatively large coefficients of friction have a relatively large tendency to bridge.
Most materials, however, when in motion are known to have a relatively smaller coefficient of friction than at rest. The present invention appreciates this fact and endeavours to reduce the coefficient of friction between bulk particles by producing relative motion therebetween.